This invention relates to telemetry systems and more particularly to such systems which can be used to gather in-flight data on the performance of weapons such as guided missiles, artillery shells, "smart bombs" and other similar projectiles. Samples of such projectiles are often withdrawn from service and subjected to flight tests to evaluate the performance of such things as fuzes, arming circuits, guidance systems, or to measure trajectory. Also, during development of weapons of these types, test firings are made to evaluate performance by measuring such things as rate of rotation, vibration, stress, and other features. Also, environmental data such as meteorological data is often gathered during such flight tests. The recent introduction of sophisticated weapons such as "smart bombs" and projectiles has lead to an increase in the amount of on-board sensor data which must be gathered during such test flights.
Prior to the present invention there were two principal methods of gathering such in-flight data. One was a hardwired telemetry system in which data was transmitted by wires from the projectile as it was being launched or fired. The wires would be severed before the projectile left the gun barrel and no further data could be obtained thereafter. This method has obvious disadvantages and limitations.
The more common prior art practice was to transmit the in-flight data to a ground station by radio. This is known as RF telemetry. However, RF telemetry has numerous disadvantages, for example it requires a transmitter with numerous subcarrier oscillators for transmitting the outputs of each sensor. Also, the bandwidth of the transmitter limits the amount of data which can be transmitted. Thus, high frequency vibrational data which exceeds the transmitter's bandwidth cannot be telemetered by this means. Also, the projectile must be modified to include the transmitting antenna. RF telemetry also requires complex and expensive manned ground station equipment for receiving and recording the transmitted data. Also, the transmission of the data means that unauthorized parties can intercept it.
The present invention comprises a telemeter system which is designed to be temporarily installed in the projectile under test and which includes circuitry for processing and recording, in a digital memory, all of the data from the sensors carried by the projectile. The development of very large-scale integrated memory chips which have large storage capacity and which also can easily be made shock and vibration resistant has made feasible the in-flight recording of data on projectiles of these types. After the flight, the projectile is recovered and the instrument package therein is interrogated and the data stored in the telemeter's memory is transferred to a light-weight portable recording instrument. The memory telemeter can be packaged in a case which includes all of the required circuitry and a battery and which is designed to withstand and function during the highshock conditions of firing, flight, and target or ground impact. This memory telemeter is simpler, less expensive, lighter in weight and more accurate than the RF telemeters described above.
Such a memory telemetry system is especially useful in artillery projectile instrumentation. It is a self-contained, shock resistant, light-weight package, usually a cylinder, which may be located in any part of the projectile. Required shell modifications are minimal and the aerodynamic characteristics of the round are virtually unaltered. As a practical matter, the warhead of an explosive shell or missile will be removed for the test and the instrument package of the present invention inserted in its place.